Shonisaurus popularis and probably Himalayasaurus tibetensis (both Late Triassic), exceeding 15m, are the largest ichthyosaurs that have been described, but there are undescribed specimens that are larger. Among the smallest ichthyosaurs is Chaohusaurus geishanensis (Early Triassic; the figure above), which probably did not reach 70 cm.

3-2. Body Weight

Body mass estimation of extinct animals is not a simple task. It usually involves many assumptions and large margins of errors. If you see some numbers with more than three digits of significant figure (for example, 1234 kg), you have a good enough reason to doubt the validity of such numbers. Scientists with conscience would more likely give such values as 1230 kg (or 1.23E3) or 1200 kg (or 1.2E3) for the same estimate, and probably with error margins.

I received so many questions asking how heavy ichthyosaurs had been. I suppose school projects ask for these values. So here are some estimates of ichthyosaurian weight that I have calculated using a computer program called PaleoMass.

Species

Fork Length (m)

Weight (kg)

Stenopterygius sp.

0.450

0.900-0.924

Stenopterygius sp.

1.19

17.1-17.5

Stenopterygius sp.

2.40

163-168

Ophthalmosaurus icenicus

4.0

930-950

Some larger ichthyosaurs were surely much heavier, but it is difficult to estimate their body mass since their whole skeletons are rare.